A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a user drives a car by the guidance produced by a navigation system. Such a navigation system detects the position of the user or user's vehicle, reads out map data pertaining to an area at the current vehicle position from a data storage medium. Alternatively, such map data can be provided to the user from a remote server through a communication network such as Internet.
When a destination is set, the navigation system starts a route guidance function for guiding a user along a calculated route from the start point to the destination. During the route guidance, the navigation system reads the nodes data from the data storage medium such as DVD and successively stores the nodes data of road segments constituting the guided route in a memory. In the actual traveling, the node series stored in the memory is searched for a portion of the guided route to be displayed in a map display area of the monitor screen, and the portion of the guided route is highlighted so as to be clearly discernible from other routes. When the vehicle is within a predetermined distance from an intersection it is approaching, a highlighted intersection diagram with an arrow indicating the direction to turn at the intersection is displayed to inform the user of the appropriate road and direction at the intersection.
FIGS. 1A-1H show an example of overall procedure and screen display involved in the navigation system. FIG. 1A shows an example of locator map screen of the navigation system when the destination is not specified. Typically, the navigation system displays a street on which the vehicle (current vehicle position VP) is running on a map image and a name of the street. When selecting a “Destination” menu on a main menu screen (not shown), the navigation system displays an “Find Destination By” screen as shown in FIG. 1B for specifying an input method for selecting the destination.
The “Find Destination By” screen of FIG. 1B lists various methods for selecting the destination. The methods include “Address” for specifying the city and address of the destination, “Intersection” for specifying the names of two streets which intersect with one another, and “Point of Interest (POI)” for selecting the programmed destination based on the name, category or telephone number. Other methods in the “Find Destination By” screen include “Recent Route” for specifying the destination based on the recent history of destinations saved in the system, “Address Book” for selecting the address of the destination out of the prescribed address list stored in the system, and “Today's Plan” for selecting two or more destinations.
When selecting, for example, the “Point of Interest (POI)” method, the navigation system displays selection methods of point of interest (POI) either by “Place Name” or “Place Type” in FIG. 1C. The “Place Name” is to specify a name of POI, and the “Place Type” is to specify a category or type of POIs. Suppose the “Place Type” is selected, the navigation system shows an “Select Category” screen such as shown in FIG. 1D.
Suppose the user selects “Restaurant”, the navigation system retrieves the POIs in the selected category, restaurant, as shown in FIG. 1E. Typically, names of POIs (restaurants) will be listed in the order of distance from the user (ex. current vehicle position). If the user selects a particular restaurant from the list, the navigation system displays a “Confirm Route” screen such as shown in FIG. 1F. In this example, the “Confirm Route” screen lists the name, address and phone number of the destination (POI specified by the user). If this is the correct destination, the user enters an “OK to Proceed” key to proceed to the next procedure.
In FIG. 1G, the navigation system calculates and determines a route to the destination, i.e., the selected POI. The navigation system determines a route to the destination based on, for example, the shortest way to reach the destination, the route using many free ways as possible or the route without using toll road, and the like. Then, the navigation system starts the route guidance as shown in FIG. 1H to guide the user along the calculated route to the destination. Typically, the navigation system shows the intersection which is highlighted to show the next turn and a direction of the turn. Such route guidance by the navigation system is also accompanied by voice instructions.
The foregoing is a typical example of using the “Point of Interest (POI)” input method of the navigation system for selecting a destination. Because the recent storage medium provides a large volume of POI data, this input method can be used in various applications. For example, suppose a user is driving a car for a relatively long trip through a calculated route to the destination, and the user wants to stop-by various places such as a gas station, restaurant, shopping mall, etc., along the route. Alternatively, the user may simply want to enjoy seeing various places along the calculated route to the destination.
Accordingly, a POI search method is proposed so that it lists points of interest that a user will encounter in following the calculated route to the destination. In this method, generally, the navigation system will detect POIs along the route by determining if POIs exist within a certain range of the calculated route. Such a situation is shown in the diagram of FIG. 2. The navigation system checks if a POI exists within a search range 16 along the calculated route 12. The search range 16 is created, for example, by incrementally shifting a search circle 15 of a predetermined diameter on the calculated route 12. Among several POIs 23a-23e, the navigation system will retrieve a POI 23b as it falls within the search range 16.
The navigation system generally lists detected POIs along the route in the order that the user will encounter them in following the calculated route, i.e., in an order of distance from the current user (vehicle) position. When the destination is located far away from the current vehicle position, POI information necessary for the user could not be detected by the navigation system. This drawback mainly stems from the decrease of performance due to the scope of search required to find all POIs along the route. For example, if the navigation system has to search all of POIs along the route to the destination which is over, for example, 200 miles away from the current position, it takes a long time to detect all of the POIs even by using a most advanced processor. Therefore, the navigation system usually has to limit the range of search to several ten miles from the current vehicle position.
In such a situation, the user is unable to fully utilize POI data since the user cannot see POIs located over 200 miles range. This poses difficulty in planning a stopover en route to a destination. For instance, the user may depart to a destination in the morning and want to decide where to take lunch in advance. In some cases, the user wants to make a stopover in a particular city for a particular event during the trip. The user may know that the vehicle will pass through countryside rich in nature, and wants to take a dinner in that region. Accordingly, there is a need for a navigation system that is capable of searching for POI information or other types of information even when they are located far away from the present vehicle location.